The Great Imitator is a phrase used for medical conditions that feature nonspecific symptoms and may be confused with a number of other diseases. Most great imitators are systemic in nature. Diseases sometimes referred to with this name include:

• Various cancers 
• Various rheumatic conditions, including, but not limited to
  • Fibromyalgia
  • Lupus erythematosus 
    • Systemic lupus erythematosus
  • Sarcoidosis